Thermal power station

ABSTRACT

The invention relates to a thermal power station and a method for storing heat by means of a steam generator a water-steam cycle which is connected to the steam generator and to a thermal store. Said thermal store comprises a first container for a heat store medium when it is cold, a second container for the heat store medium when it is hot, and a heat exchanger which is connected to the two containers and which is connected to the heat-steam cycle via a water-steam feed line and a water-steam discharge line. The thermal store has an additional heat exchanger which is connected to the two containers, an air feed line and an air discharge line being provided, the air discharge line being connected to the combustion air feed line leading to the combustion chamber.

The invention relates to a thermal power station having a steam generator, which comprises a combustion chamber with a feed for combustion air, having a water-steam cycle, which is connected to the steam generator, and having a thermal store, which is connected to the water-steam cycle.

The invention also relates to a method for storing heat in a thermal power station which comprises a steam generator with a combustion chamber and a feed for combustion air and water-steam cycle.

Due to the ongoing development of renewable energies, both overcapacities and undercapacities of the electrical power can occur over the course of time. The fluctuations are compensated for with the aid of conventional power stations. For this purpose, fossil-fired power stations, in particular coal-fired power stations, with steam generators are often used, however these are associated with the disadvantage that the amount of power to be delivered to the power grid cannot be altered arbitrarily or sufficiently quickly.

For this reason, a generic thermal power station has already been proposed in DE 10 2012 103 617 A1, with which an adaptation to the fluctuating feed-in demand of the connected electricity grid is made possible. For this purpose, thermal energy can be decoupled as required from the water-steam cycle of the power station directly or via a heat exchanger into a thermal store. The steam therefore does not necessarily have to be conducted via the turbine set or turbo set for electricity generation, but alternatively can be guided into the thermal store in order to deliver thermal energy. With constant steam generation, the amount of steam used for electricity generation can be reduced and therefore the amount of electricity fed from the power station into the grid can be controlled as required. If the power station then has to be started up again, the heat stored in the thermal store can be decoupled into the steam generator. The thermal store can consist of two containers operated in alternation and containing a store medium, for example melted salt. In one embodiment the thermal store is thermally coupled to a second heat exchanger which is in turn coupled thermally to a second steam generator. A turbine set or turbo set with connected generator is associated with the second steam generator. The second heat exchanger is preferably operated if undercapacities in the electricity grid are to be compensated. Furthermore, it was mentioned generally in DE 10 2012 103 617 A1 that the thermal store can be connected to an air preheating device for preheating combustion air. However, no practicable solution was described regarding how the decoupling of the thermal energy stored in the thermal store via the air preheating device could function.

WO 2013/014664 A2 discloses another kind of hybrid power station, which mixes thermal energy from different energy sources, stores it and provides it for a generator.

WO 2014/076849 A1 discloses another kind of device for providing thermal energy for a generator, wherein energy is conducted directly to the generator via a heat carrier fluid cycle and thermal energy is fed to a storage tank via a separate, second heat carrier fluid cycle which thermal energy is conducted to the generator as required.

EP 2 562 373 A1 presents an IGCC (integrated gasification combined cycle) process, in which some of the thermal energy of the synthesis gas created by said process is converted into electrical energy via a Rankine cycle.

WO 2014/044549 A2 furthermore discloses a different kind of method for charging and discharging a thermal store, in which the corresponding cycles are designed as a Rankine cycle. In the charging cycle heat is transferred from a gaseous working fluid via a first heat exchanger to a liquid storage medium of the thermal store.

The object of the present invention is therefore that of creating a thermal power station of the kind mentioned in the introduction of simple design, in which the thermal energy stored in the thermal store can be fed back as efficiently as possible.

This object is achieved by a thermal power station having the features of claim 1 and a method for storing heat in a thermal power station having the features of claim 11.

In accordance with the invention the thermal store comprises a first container for a heat store medium when it is cold, a second container for the heat store medium when it is hot, and a heat exchanger which is connected to the first container and to the second container, wherein the heat exchanger is connected to the water-steam cycle via a water-steam feed line and a water-steam discharge line, wherein the heat store medium can be conveyed from the first container via the heat exchanger to the second container in order to absorb heat from the water and steam, wherein the thermal store comprises an additional heat exchanger which is connected to the first container and to the second container, wherein an air feed line for feeding air into the additional heat exchanger and an air discharge line for discharging the air from the additional heat exchanger are provided, wherein the heat store medium can be conveyed from the second container via the additional heat exchanger to the first container in order to dissipate heat to the air, wherein the air discharge line is connected to the feed for combustion air into the combustion chamber.

When charging the thermal store, the heat store medium is guided from the first container via the heat exchanger into the second container, wherein the heat store medium is heated by absorbing heat from the water and steam. The water and steam is preferably branched from the water-steam cycle between the steam generator and the turbine.

When charging the thermal store the heat store medium itself is advantageously moved, whereby the heat exchange can be particularly efficient. When discharging the thermal store the heat store medium is conveyed in the opposite direction from the second container via an additional heat exchanger to the first container. During this process, an airflow is guided through the additional heat exchanger, at which the heat store medium outputs its heat. The heat store medium is thus cooled, and the airflow is heated accordingly. The airflow is then fed to the feed into the combustion chamber of the steam generator, such that the thermal energy stored in the thermal store is in turn available for the steam generation. Interventions involving the complex water-steam cycle of the thermal power station can thus be minimised advantageously. The steam generator can have a wide range of different embodiments, however these have long been known in the prior art and therefore do not require any further explanations. The steam generator can therefore comprise in particular an evaporator, a superheater, a feed water preheater, an air preheater, and a furnace, for example for coal, oil, biomass or gas. It is in any case essential that the charging of the thermal store in the heat exchanger occurs by means of water and steam, and the discharging of the thermal store in the additional heat exchanger occurs by means of air. The heat exchanger and the additional heat exchanger are structurally separate from one another here. The heat exchanger and the additional heat exchanger can thus be adapted selectively to the different requirements of the charging process and discharging process and also to the various types of heat carrier media (water and steam in the case of the heat exchanger, air in the case of the additional heat exchanger). Since air has a much lower heat transfer coefficient than water and steam, the required heat exchange surfaces in the additional heat exchanger are much greater than in the heat exchanger with identical heat flow and identical temperature difference. By using separate heat exchangers, these differences can be easily taken into account. If, for example, the water and steam in the heat exchanger and the air in the additional heat exchanger are guided through line arrangements, in particular tube bundles, the cross-section of the line arrangement in the additional heat exchanger can thus be much greater than the cross-section of the line arrangement in the heat exchanger.

In accordance with a particularly preferred embodiment a first shut-off device is provided between the first container and the heat exchanger and/or a second shut-off device is provided between the first container and the additional heat exchanger and/or a third shut-off device is provided between the second container and the heat exchanger and/or a fourth shut-off device is provided between the second container and the additional heat exchanger. The aforesaid shut-off devices can be switched between an open position enabling the passage of the heat store medium and a blocking position blocking the passage of the heat store medium. In a preferred embodiment the first shut-off device and the third shut-off device in the charging state of the thermal store are arranged in the open position, such that the heat store medium can flow from the first container via the heat exchanger to the second container. By contrast, at least the second shut-off device, in particular also the fourth shut-off device, is arranged in the closed position in the charging state of the thermal store, such that the heat store medium cannot pass from the first container into the heat exchanger. In the discharging state of the thermal store the switched positions of the shut-off devices can be reversed. Thus, at least the third shut-off device, in particular also the first shut-off device, in the charging state of the thermal store can be arranged in the closed position, such that the heat store medium cannot pass from the second container into the heat exchanger. By contrast, the fourth shut-off device and the second shut-off device are arranged in the open position in the discharging state of the thermal store, such that the heat store medium can flow from the second container via the additional heat exchanger into the first container.

Solid particles, in particular sand or corundum, are preferably arranged as heat store medium in the first and/or second container. This embodiment in particular is associated with the advantage that these heat store media can be used at much higher temperatures. These materials also have particularly high long-term stability and can be acquired economically.

In a preferred embodiment the additional heat exchanger is designed for discharging the thermal store for a direct heat exchange between the solid particles and the air. The surfaces of the solid particles advantageously form large heat exchange surfaces which enable an effective dissipation of heat to the air. By contrast, the heat exchanger for charging the thermal store is preferably designed for indirect heat transfer between the heat store medium and the water and steam, for example by means of a line arrangement.

An embodiment in which a fluidised bed heat exchanger is provided each as heat exchanger and/or as additional heat exchanger is particularly preferred. When discharging the thermal store, the air required for the fluidisation of the heat store medium in the additional heat exchanger can additionally be used as heat carrier medium for the withdrawal of thermal energy. The low heat transfer coefficient of air can advantageously be compensated by the very large heat exchanger surfaces in the fluidised layer. Here, the volume flow of the air in the additional heat exchanger during discharging can be much higher than the volume flow of a fluidisation air of the heat exchanger during charging of the thermal store. In the additional heat exchanger for discharging the thermal store, a direct heat exchange can take place between the air and the heat store medium. By contrast, an indirect heat exchange preferably can be provided between the water and steam and the heat store medium in the heat exchanger for charging the thermal store. For this purpose, the water-steam feed line and the water-steam discharge line can be connected within the heat exchanger by a line arrangement, in particular by a tube bundle. The line arrangement comprises heat exchange surfaces for heat exchange between the heat store medium and the water and steam.

As is generally usual in thermal power stations, an air preheater for preheating the combustion air is preferably provided for the combustion chamber. The air preheater can be connected on the one hand to a fresh air inlet and on the other hand to an output line for waste combustion gases leading away from the combustion chamber of the steam generator, such that the combustion air flowing from the fresh air inlet into the air preheater is preheated by heat exchange with the waste combustion gases before the combustion air enters the combustion chamber.

In a structurally simple variant the air feed for the additional heat exchanger is branched from a connection line between the air preheater and the combustion chamber. A shut-off element is preferably provided between the air preheater and the air feed for the additional heat exchanger which shut-off element preferably is adjustable substantially continuously between an open position allowing the airflow to pass through and a closed position blocking the passage of the airflow. In addition, the connection line preferably comprises a further shut-off element which likewise is adjustable preferably substantially continuously between an open position and a closed position. The volume flow for the air feed into the additional heat exchanger can thus be adjusted. In the discharging state of the thermal store a first volume flow can be branched from the connection line via the bypass line into the air feed for the additional heat exchanger, wherein the first volume flow is designed to enable the withdrawal of the thermal energy of the heat store medium in the airflow. In this embodiment the air preheater and the air feed for the additional heat exchanger in the discharging state of the thermal store are therefore connected in series.

In the charging state of the thermal store, a second volume flow can be branched from the connection line into a further air feed for the heat exchanger in a preferred embodiment in order to enable a fluidisation of the heat store medium in the heat exchanger. The second volume flow of the branched airflow can be lower than the first volume flow, since the air in the heat exchanger can be used merely for fluidisation, but not for heat absorption.

In a further preferred variant, the air preheater is connected to a fresh air inlet, wherein the air feed for the additional heat exchanger is connected to a fluidisation air inlet. In this variant the air feed for the additional heat exchanger is connected to a dedicated fluidisation air inlet, via which an airflow for the additional heat exchanger can be provided independently of the fresh air inlet for the air preheater. An adaptation to the different pressure conditions and mass flows can thus be achieved advantageously. In this embodiment the flow path between the fluidisation air inlet and the air feed for the additional heat exchanger is preferably free from an air preheater, such that air at ambient temperature can be introduced into the additional heat exchanger. This has the advantage that the temperature spread for the cooling of the heat store medium in the heat exchange with the air can be maximised.

In order to provide the necessary volume flows in the charging and discharging state of the thermal store, it is favourable if the fresh air inlet is connected to a fresh air fan and/or the fluidisation air inlet is connected to a fluidisation fan. The volume flows at the fresh air inlet and at the fluidisation air inlet can therefore advantageously be controlled independently of one another.

In order to be able to guide the waste combustion gases in the charging state of the thermal store via the air preheater and to ensure effective cooling of the waste combustion gases in the discharging state, an output line for discharging waste combustion gases from the combustion chamber is preferably provided, which output line comprises a line portion leading into the air preheater and a further line portion leading into a water preheater of the water-steam cycle.

In a preferred embodiment an electrical heating element, in particular a resistance heater, is installed in the heat exchanger. The electrical heating element can be connected in particular to an electricity grid in order to use excess power to heat the heat store medium. In this embodiment the thermal power station comprises at least a first and a second operating state. In the first operating state the heat store medium, as described before, can be heated via the water and steam and cooled via the air. In the second operating state the electrical heating element is switched on in order to perform or support the heating of the heat store medium alternatively or in parallel to the absorption of heat from the water and steam, for example in order to reach an optimal operating temperature.

The method according to the invention for storing heat of a thermal power station which comprises a steam generator with a combustion chamber and a feed for combustion air and a water-steam cycle comprises at least the following steps:

-   -   conveying a heat store medium when it is cold from a first         container via a heat exchanger to a second container,     -   conducting water and steam from the water-steam cycle through         the heat exchanger with heat being exchanged with the heat store         medium,     -   conveying the heat store medium when it is hot from the second         container via an additional heat exchanger into the first         container,     -   conducting air through the additional heat exchanger with heat         being exchanged with the heat store medium when it is hot, and     -   feeding the air as combustion air into the combustion chamber.

The invention will be explained in greater detail hereinafter with reference to preferred exemplary embodiments, but is not limited thereto. In the drawing:

FIG. 1 shows a block diagram of a thermal power station according to the invention, in which the thermal energy of a steam flow branched between a steam generator and a turbine is dissipated in a heat exchanger to a powdery heat store medium, wherein the stored thermal energy is fed back as required in an additional heat exchanger from the heat store medium into an airflow for a combustion chamber of the steam generator;

FIG. 2 shows a block diagram of the essential components of the thermal power station according to FIG. 1; and

FIG. 3 shows a block diagram of a further thermal power station according to the invention.

FIG. 1 schematically shows a thermal power station 1 in the form of a steam power station with a steam generator 2 which comprises a combustion chamber 3 (shown separately for the sake of clarity) with a feed 4 for combustion air and a feed 39 for fuel. A water-steam cycle 5 is connected to the steam generator 2. The steam generator 2 is connected via a first valve 6 to a turbine 7, to which there is connected a generator G. The water-steam cycle 5 additionally comprises further components provided as standard in the prior art, in particular a condenser 8, a feedwater pump 9 and a feed water preheater 10.

The thermal power station 1 additionally comprises a thermal store 11 shown in a simplified manner in FIG. 1 and visible in detail in FIG. 2 for buffering thermal energy of the steam guided in the water-steam cycle 5.

As can be seen in particular from FIG. 2, the thermal store device 11 comprises a first container 12 for a heat store medium when it is cold, a second container 13 for the heat store medium when it is hot and a heat exchanger 14 connected to the first container 12 and to the second container 13. A bed of solid particles, in particular sand, is provided as heat store medium. The heat exchanger 14 is connected to the water-steam cycle 5 via a water-steam feed line 15 and a water-steam discharge line 16. A pump 17 visible in FIG. 1 is arranged in the water-steam discharge line 16 in order to compensate for any pressure losses. A valve 40 is provided in the water-steam feed line 15. The heat store medium can be conveyed from the first container 12 via the heat exchanger 14 to the second container 13 in order to absorb heat from the water and steam.

In addition, the thermal store 11 comprises an additional heat exchanger 18, which is connected to the first container 12 and to the second container 13. An air feed 19 for feeding air into the additional heat exchanger 18 and an air discharge line 20 for discharging the air once it has passed through the additional heat exchanger 18 is also provided. In a discharging process the heat store medium is conveyed from the second container 13 via the additional heat exchanger 18 to the first container 12 in order to dissipate heat to the air. The air discharge line 20 is connected to the feed 4 into the combustion chamber 3, such that the air heated in the additional heat exchanger 18 in the heat exchange with the heat store medium can be introduced as combustion air into the combustion chamber 3.

As can be seen from FIG. 2, a first shut-off device 21 is provided between the first container 12 and the heat exchanger 14, a second shut-off device 22 is provided between the first container 12 and the additional heat exchanger 18, a third shut-off device 23 is provided between the second container 13 and the heat exchanger 14, and a fourth shut-off device 24 is provided between the second container 13 and the additional heat exchanger 18.

In the shown embodiment, fluidised bed heat exchangers are provided as heat exchanger 14 and as additional heat exchanger 18. In this case the heat exchanger 14 comprises a fluidisation air feed (not shown in FIG. 2), by means of which the bed of heat store medium can be fluidised. The fluidisation air, however, is not provided as a heat carrier medium for charging the heat store medium in the heat exchanger 14. The heat is dissipated to the heat store medium substantially completely by the steam fed via the water-steam feed line 15.

As can be seen from FIG. 1, the thermal power station 1 comprises an air preheater 25 for preheating the combustion air prior to entry into the combustion chamber 3. The air preheater 25 is connected via a fresh air fan 26 to a fresh air inlet 27. The waste combustion gases generated in the combustion chamber 3 are delivered into an output line 28, which is connected to the air preheater 25. A heat exchange between the waste combustion gases in the output line 28 and the fresh air coming from the fresh air inlet 27 occurs in the air preheater 25, such that the waste combustion gases are cooled and the fresh air is preheated accordingly. The cooled waste combustion gases can then be released into the surrounding environment.

In the variant of FIG. 1 a bypass line 29 leads away from a connection line 30 between the air preheater 25 and the combustion chamber 3 which bypass line 29 is connected to the air feed 19 into the additional heat exchanger 18. The air discharge line 20 from the additional heat exchanger 18 leads back into the connection line 30. A shut-off element 31 is arranged in the bypass line 29. An additional shut-off element 32 is arranged in the connection line 30. With the aid of the shut-off element 31 and the additional shut-off element 32, the volume flow in the bypass line 29 can be adjusted. In the discharging state a volume flow of air that is much higher as compared to a fluidisation volume flow is guided via the bypass line 29 into the additional heat exchanger 18, so that the airflow can function as a heat carrier medium for the thermal energy stored in the heat store medium.

An electrical heating element in the form of a resistance heater 40 is additionally visible in FIG. 2 schematically and is guided into the heat exchanger 14. The resistance heater 40 is connected to a power grid in order to be able to heat the heat store medium in the heat exchanger 14 as required by conversion of electrical energy into thermal energy. The resistance heater 40 can be activated alternatively or additionally to the water-steam cycle 5, for example so as to set an optimal operating temperature of the heat store medium.

FIG. 3 shows an alternative variant which differs from the embodiment of FIG. 1 in respect of the discharging process. Merely the differences between the embodiment according to FIG. 3 and that of FIG. 1 will be discussed hereinafter.

According to FIG. 3 the air feed 19 for the additional heat exchanger 18 is connected to a fluidisation air inlet 33 separate from the fresh air inlet 27. The key advantage of this embodiment lies in the possibility of being able to use fans or compressors especially adapted to the volume flows and pressures. In addition, the air preheater 25 can be decoupled from the higher pressure after the fluidisation air inlet 33, which leads to a more economical embodiment of the air preheater 25. The fluidisation air inlet 33 is connected in the shown embodiment to a fluidisation fan 34. In this embodiment the output line 28 comprises a line portion 35 leading into the air preheater 25 and a further line portion 37 leading into a water preheater 36 of the water-steam cycle 5. In the charging state the waste combustion gases are guided via the line portion 35 to the air preheater 25. Once the waste combustion gases have cooled in the air preheater 25, the waste combustion gases are discharged into the surrounding environment. In the discharging state the waste combustion gases are guided via the line portion 37 into the water preheater 36 of the water-steam cycle 5. The waste combustion gases can thus be effectively cooled during the discharge in the switched-off state of the fresh air fan 26. In order to be able to conduct the waste combustion gases to the air preheater 25 during the charging process and to the water preheater 36 during the discharging process, a shut-off valve 38 is arranged in each of the line portions 35 and 37.

A method having at least the following steps can therefore be carried out: conveying a heat store medium when it is cold from a first container 12 via a heat exchanger 14 to a second container 13, and in the meantime conducting water and steam of the water-steam cycle 5 of the thermal power station 1 through the heat exchanger 14 with dissipation of heat to the heat store medium, conveying the heat store medium when it is hot from the second container 13 via the additional heat exchanger 18 into the first container 12, and in the meantime conducting air through the additional heat exchanger with absorption of heat from the heat store medium when it is hot, and then feeding the air as combustion air into the combustion chamber 3. 

1. A thermal power station having a steam generator, which comprises a combustion chamber with a feed for combustion air, having a water-steam cycle, which is connected to the steam generator, and having a thermal store, which is connected to the water-steam cycle, wherein the thermal store comprises a first container for a heat store medium when it is cold, a second container for the heat store medium when it is hot, and a heat exchanger which is connected to the first container and to the second container, wherein the heat exchanger is connected to the water-steam cycle via a water-steam feed line and a water-steam discharge line, wherein the heat store medium can be conveyed from the first container via the heat exchanger to the second container in order to absorb heat from the water and steam, wherein the thermal store comprises an additional heat exchanger which is connected to the first container and to the second container, wherein an air feed line for feeding air into the additional heat exchanger and an air discharge line for discharging the air from the additional heat exchanger are provided, wherein the heat store medium can be conveyed from the second container via the additional heat exchanger to the first container in order to dissipate heat to the air, wherein the air discharge line is connected to the feed for combustion air into the combustion chamber.
 2. The thermal power station according to claim 1, wherein a first shut-off device is provided between the first container and the heat exchanger and/or a second shut-off device is provided between the first container and the additional heat exchanger and/or a third shut-off device is provided between the second container and the heat exchanger and/or a fourth shut-off device is provided between the second container and the additional heat exchanger.
 3. The thermal power station according to claim 1, wherein solid particles, including sand or corundum, are arranged as heat store medium in the first and/or second container.
 4. The thermal power station according to claim 1, wherein a fluidised bed heat exchanger is provided each as the heat exchanger and/or as the additional heat exchanger.
 5. The thermal power station according to claim 1, wherein air preheater for preheating the combustion air for the combustion chamber is provided.
 6. The thermal power station according to claim 5, wherein the air feed line for the additional heat exchanger is branched from a connection line between the air preheater and the combustion chamber.
 7. The thermal power station according to claim 5, wherein the air preheater is connected to a fresh air inlet, wherein the air feed line for the additional heat exchanger is connected to a fluidisation air inlet.
 8. The thermal power station according to claim 7, wherein the fresh air inlet is connected to a fresh air fan and/or the fluidisation air inlet is connected to a fluidisation fan.
 9. The thermal power station according to claim 6, wherein an output line for discharging waste combustion gases from the combustion chamber is provided, where the output line comprises a line portion leading into the air preheater and an additional line portion leading into a water preheater of the water-steam cycle.
 10. The thermal power station according to claim 1, wherein an electrical heating element, including a resistance heater, is installed in the heat exchanger.
 11. A method for storing heat in a thermal power station which comprises a steam generator with a combustion chamber and a feed for combustion air and a water-steam cycle, said method having the following steps: conveying a heat store medium when it is cold from a first container via a heat exchanger to a second container, conducting water and steam from the water-steam cycle (5) through the heat exchanger with heat being exchanged with the heat store medium, conveying the heat store medium when it is hot from the second container via an additional heat exchanger into the first container, conducting air through the additional heat exchanger with heat being exchanged with the heat store medium when it is hot, and feeding the air as combustion air into the combustion chamber. 